Storm the Castle B

[wlsguy]

Every time we try our buleprints, they never work. We are using balsa wood and latex rubber bands. We dont understand but it keeps plunging into the ground. We have a hypothesis that maybe the handle is too flimsy, but after making adjustment hundreds of times, it doesn't help. Any ideas anyone

For those who are having trouble (or haven't started). Check the WIKI. It has the instructions for the basic T shaped treb.
Also check the following site from the North Carolina Science Olympiad. It has a basic (and adjustable) T treb.
http://www.sciencenc.com/event-help/stormthecastle.php

Both of these designs are fundamentally the same. They are also proven to give you something that works.
It may also help you troubleshoot your own machine

[aramc]

Hi i have couple of questions:

on the instructions it says the following regarding the arm.

"about one inch from each end drill a hole the size of your bolt eyelets all the way through the top and bottom. These holes should be parallel to each other, and skew to the axle hole. "

However the rules state that "the edge of the hole must be no more than 1 cm from the edge of the material."

i am confused as the above two seem to contradict.

Also, i am not clear on the function of the nail on the arm. it says the following

"take one nail and tape it on the long side of your arm, point facing off the end, and on the top side.

and to then on the sling string it says" tie the other string into a loop that you slip on the nail. "

Is this not going to pull out the nail when the arm is released? how do you adjust the angle? also can a funnel do the trick instead of a sling?

thanks in advance

[wlsguy]

"about one inch from each end drill a hole the size of your bolt eyelets all the way through the top and bottom. These holes should be parallel to each other, and skew to the axle hole. "

The key is to put one of the eyelets at each end of the arm. When the arm is in position, these eyelets should face downward. the one at the counterweight side will be used to hold the counterweight itself and needs to have a hole ~ 10mm for the counterweight hook to fit through. The other is at the throwing end of the arm. It is used with the other 2 screw eyelets from 8) step 8. The release nail will go through all three of them and will keep the arm from moving until the string with the nail is pulled.

" tie the other string into a loop that you slip on the nail. "

The instructions use the taped nail as the release pin. Taping it will allow you to adjust the angle slightly to get a good launch. I actually prefer to screw the pin to the end of the arm so the release can be adjusted according to the projectile and counterweight provided. This involves bending a pin out of coathanger. Generally something around 30mm with a loop on the end will work. It should look something like a 6 but without the bend at the top of the number. This is then attached to the arm with a small bolt and nut and tightened down (but not too tight). The pin can then be adusted to allow for the best release.

As far as using a funnel.
Yes, it works, but it will throw significantly less. The additional length of the sling makes the arm much more efficent and allows the device to throw much farther. This is what made it such an effective invention in the Middle Ages when catapults (with funnels) were the primary siege weapon.

tell me if you need a better explaination or photos. I can probably post something if needed.

[aramc]

Thanks for the reply. We pretty much have followed the instructions, but still having trouble with the Taped Pin. We tried it yesterday, and on the first try, the projectile did not even release from the pouch. Since the string was as long as the arm, we figured it was too long so we cut it half. Well that helped, except the projectile went the opposite direction lol.

we tried adjusting the string length but finally just attached a funnel. that worked really well, but as you stated, the distance was very less.

So, in our minds, we thought the only two input variables are the CW and Projectile, and the distance the output. But now i am hearing the pin angle may be an variable?

we would love if you could post some pics. especially to help around sling (closeup..
Length of the string?
One end of the string is tied to the eyelet (Permanent)
the other end of the string is made into loop and slips over the taped pin
Thank you again.

[aramc]

Just now uploaded a picture to the Pic Gallery. Shows a closeup of the taped Pin, and Sling.. as you can see our string is short. Thanks

[brobo]

Well, I've procrastinated long enough, and it's about time to start working on my trebuchet again. At the last tournament it didn't do to well, so I wanted to describe what I plan on doing to improve it and see what everyone else thought.
I built a standard FAT trebuchet, with the rails being about half way up the vertical guides. Watching it later (and looking at other teams' designs) I decided that I should move the rails up to about 2/3 - 3/4 of the way up the vertical guides so that the arm didn't have a total inversion... the arm was more of flipping than moving and I think I was losing a lot of power. The second thing I want to do is remake the arm so it is larger. Not longer, but thicker. If force = mass * acceleration and I can't add any acceleration (all mighty ENERGY RULE) than I can at least add mass. As long as the arm was balanced it shouldn't violate the energy rule, and the throw would get a lot more force to it. Lastly, I want to make the track wider and get some larger wheels. Right now my wheels aren't always staying on the track, and I think it's because my wheels are really small and the track is really thin.

Any input would be greatly appreciated!

[starpug]

Well, I've procrastinated long enough, and it's about time to start working on my trebuchet again. At the last tournament it didn't do to well, so I wanted to describe what I plan on doing to improve it and see what everyone else thought.
I built a standard FAT trebuchet, with the rails being about half way up the vertical guides. Watching it later (and looking at other teams' designs) I decided that I should move the rails up to about 2/3 - 3/4 of the way up the vertical guides so that the arm didn't have a total inversion... the arm was more of flipping than moving and I think I was losing a lot of power. The second thing I want to do is remake the arm so it is larger. Not longer, but thicker. If force = mass * acceleration and I can't add any acceleration (all mighty ENERGY RULE) than I can at least add mass. As long as the arm was balanced it shouldn't violate the energy rule, and the throw would get a lot more force to it. Lastly, I want to make the track wider and get some larger wheels. Right now my wheels aren't always staying on the track, and I think it's because my wheels are really small and the track is really thin.

Any input would be greatly appreciated!

Making the arm thicker to add force would be a good idea if the projectile wasn't in a sling (assuming you're using one since it adds distance) and in fact would be harmed by a heavier arm as it would decrease the the distance your device would throw. A heavier arm decreases acceleration, so what you gain in mass you loose in acceleration. You want to decrease the weight of your arm from my experience.

Think of it this way, what if I made your arm three pounds heavier then told you to throw a ball, do you think you would be able to throw it farther then if you didn't have an arm that was three pounds heavier?

I don't know the exact physics behind this, I'm just speaking from experience.

[brobo]

Well, I've procrastinated long enough, and it's about time to start working on my trebuchet again. At the last tournament it didn't do to well, so I wanted to describe what I plan on doing to improve it and see what everyone else thought.
I built a standard FAT trebuchet, with the rails being about half way up the vertical guides. Watching it later (and looking at other teams' designs) I decided that I should move the rails up to about 2/3 - 3/4 of the way up the vertical guides so that the arm didn't have a total inversion... the arm was more of flipping than moving and I think I was losing a lot of power. The second thing I want to do is remake the arm so it is larger. Not longer, but thicker. If force = mass * acceleration and I can't add any acceleration (all mighty ENERGY RULE) than I can at least add mass. As long as the arm was balanced it shouldn't violate the energy rule, and the throw would get a lot more force to it. Lastly, I want to make the track wider and get some larger wheels. Right now my wheels aren't always staying on the track, and I think it's because my wheels are really small and the track is really thin.

Any input would be greatly appreciated!

Making the arm thicker to add force would be a good idea if the projectile wasn't in a sling (assuming you're using one since it adds distance) and in fact would be harmed by a heavier arm as it would decrease the the distance your device would throw. A heavier arm decreases acceleration, so what you gain in mass you loose in acceleration. You want to decrease the weight of your arm from my experience.

Think of it this way, what if I made your arm three pounds heavier then told you to throw a ball, do you think you would be able to throw it farther then if you didn't have an arm that was three pounds heavier?

I don't know the exact physics behind this, I'm just speaking from experience.

Cool, thanks for the heads up. I would you something as thin as the shaft from a golf club, but I don't know how to attatch the wheels to something like that... how would you put an axle through something that thin so it could also support the falling counterweight more than a few times?
Also, what are people using as their axle? I'm using a thick wooden dowel which I don't think is the best idea because it keeps breaking.

[fizwiz]

First shots this past weekend. No real fine tuning.

Counter weight = 2.5kg
Projectile = golf ball (46g)
Distance ~ 20m

Am I headed in the right direction?

[starpug]

Well, I've procrastinated long enough, and it's about time to start working on my trebuchet again. At the last tournament it didn't do to well, so I wanted to describe what I plan on doing to improve it and see what everyone else thought.
I built a standard FAT trebuchet, with the rails being about half way up the vertical guides. Watching it later (and looking at other teams' designs) I decided that I should move the rails up to about 2/3 - 3/4 of the way up the vertical guides so that the arm didn't have a total inversion... the arm was more of flipping than moving and I think I was losing a lot of power. The second thing I want to do is remake the arm so it is larger. Not longer, but thicker. If force = mass * acceleration and I can't add any acceleration (all mighty ENERGY RULE) than I can at least add mass. As long as the arm was balanced it shouldn't violate the energy rule, and the throw would get a lot more force to it. Lastly, I want to make the track wider and get some larger wheels. Right now my wheels aren't always staying on the track, and I think it's because my wheels are really small and the track is really thin.

Any input would be greatly appreciated!

Making the arm thicker to add force would be a good idea if the projectile wasn't in a sling (assuming you're using one since it adds distance) and in fact would be harmed by a heavier arm as it would decrease the the distance your device would throw. A heavier arm decreases acceleration, so what you gain in mass you loose in acceleration. You want to decrease the weight of your arm from my experience.

Think of it this way, what if I made your arm three pounds heavier then told you to throw a ball, do you think you would be able to throw it farther then if you didn't have an arm that was three pounds heavier?

I don't know the exact physics behind this, I'm just speaking from experience.

Cool, thanks for the heads up. I would you something as thin as the shaft from a golf club, but I don't know how to attatch the wheels to something like that... how would you put an axle through something that thin so it could also support the falling counterweight more than a few times?
Also, what are people using as their axle? I'm using a thick wooden dowel which I don't think is the best idea because it keeps breaking.

You would have to use a rather thin axle, or you could find something that's total diameter is big but it's got thin walls and is strong. There are some pics on the photo gallery that show two parted arms (my best guess would be the top is a golf shaft or something and the bottom is a piece of aluminum with the axle through it), you could try that. If you have the money and ability to go out and buy a piece of Carbon fiber tubing and machine that into a working arm, I would highly advise that. Admittedly, there is a limit to how low you can go in terms of arm weight without going into space age materials like Carbon Fiber

First shots this past weekend. No real fine tuning.

Counter weight = 2.5kg
Projectile = golf ball (46g)
Distance ~ 20m

Am I headed in the right direction?

I would say in the right direction, but when I did this even when I was in B division in 7th grade, we were throwing 30 meters easily with 3kg and a golf ball. The arm length may be shorter then it was then, which lowers distances, but I'd say if you can get into the 30s at max settings you'll probably be medaling at most invitationals, regionals, and probably all but the most competitive states (OH, NY, PA).